Selectively Infiltrated PCF for Directional Bend Sensing With Large Bending Range

A directional bend sensor based on selectively infiltrated photonic crystal fiber is demonstrated. The device is fabricated by use of femtosecond laser micromachining technique and fusion splicing of photonic crystal fiber with single-mode fiber. By infiltrating refractive index liquid into one of the air holes of the photonic crystal fiber, the core mode can be coupled into the higher order liquid rod mode, thus producing a resonant dip in the transmission spectrum of the device. Such a dip wavelength is sensitive to both the bending curvature and the direction, and has a linear response to curvature within a large range from 0 to 10.7 m^-1.